Where possible moved redundent C header includes from headers to source files

src/osgDB/Field.cpp

@@ -10,13 +10,15 @@
  * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the 
  * OpenSceneGraph Public License for more details.
 */
-#include <string.h>
 
 #include <osg/Notify>
 #include <osg/Math>
 
 #include <osgDB/Field>
 
+#include <string.h>
+#include <stdlib.h>
+
 using namespace osgDB;
 using namespace std;